Line a baking sheet with aluminum foil and spray lightly with non-stick cooking spray.
In a large saucepan, combine the sugar, 1/2 cup water and citric acid. Stir to dissolve and heat over medium-high heat to boiling, stirring frequently. Brush down, with a wet pastry brush, any sugar crystals that may stick to the side of the pan. This, if done, will prevent the sugar crystals from being reintroduced to the boiled sugar and causing it to crystalize (thus making it unusable).
Monitor the temperature of the sugar and continue to boil until it reaches 230°F.
Once the mixture reaches 200°F, begin to cook the cornstarch mixture in a separate pot.
Combine the remaining water, the cornstarch and cream of tartar with a whisk and bring to a boil over med-high heat. The mixture should thicken and begin to look like vaseline (or petroleum jelly).
Once the cornstarch mixture is cooked, and the sugar has reached 230°F, CAREFULLY and slowly pour the sugar mixture into the cornstarch mixture, whisking constantly. The sugar will cause severe burns if it comes into contact with your skin, so please, be careful.
Return the mixture to the stove and continue to cook for 20 minutes on low. the mixture will take on a golden yellow color and become very thick- like a paste.
Once the mixture has thickened, add the rosewater flavoring and the red food coloring. Stir to incorporate fully.
Carefully, pour the mixture into your prepared pan and spread out evenly.
Allow to sit for 12-24 hours, uncovered to prevent sweating (or a buildup of moisture).
After the rest period, dust the surface of your counter generously with powdered sugar using a sifter.
Remove the loukum from the pan by lifting the foil out, and flip the loukum onto the powdered surface carefully. Remove the foil and discard.
Generously dust the other side of the loukum with more powder sugar (this will help your loukum from sticking to everything).
Using a very sharp knife with a thin, oiled blade (use a flavorless oil like canola), cut the loukum into 1 inch squares.
Dust each square liberally with powdered sugar and place onto a serving dish.
Loukum is best enjoyed the same day or within 24 hours.
Store uncovered in a cool, dry area.